A power control unit installed in a vehicle such as a hybrid vehicle includes a battery module and an inverter. The inverter in general includes a high-power semiconductor element to increase the output. Such an inverter generates a large amount of heat due to power loss. For this reason, the power control unit is provided with an independent cooling system.
One example of cooling systems for a power control unit adopts both water-cooling and air-cooling types. The water cooling device cools an inverter of the power control unit. The water cooling device includes a circulation path, through which liquid cooling medium circulates, an electric pump for circulating the cooling medium, and a radiator for cooling the cooling medium. An electric fan for accelerating radiation of heat is arranged on a lateral surface of the radiator. The air cooling device cools a battery module including a plurality of cells. The air cooling device includes an electric fan for delivering air between the cells.
The occurrence of an abnormality in the cooling system complicates maintaining the inverter and the battery module at a temperature in an adequate temperature range. For example, if an abnormality occurs in an electric pump and an electric fan for the inverter, the temperature of cooling medium may exceed an upper limit to cause unfavorable effect on the semiconductor element. If an abnormality occurs in an electric fan for the battery module, increase in the temperature may greatly change the battery characteristics. Thus, prompt detection of an abnormality in the cooling system is necessary for the power control unit to function normally.